I was suggested to use an iron core for an inductor. I found that it has low permeabilty and good stability, but how does that make it a good material for the core. And is there a way to figure out the saturation condition for it?
The one i am using is: http://www.micrometals.com/pcparts/torcore5.html - T-130 - 52
Most applications of iron powder cores are substitutions of inductors made of ferrite cores. These applications include DC/DC converter output filter inductors and power factor correction inductors.
In these applications you need the energy storage capability (proportional to \$ B \times H \$; all quantities are magnitudes) of the inductor core. Ferrite cores have a high permeability so you need to introduce an air gap to reduce this permeability, thus increasing the magnetic field \$H\$ strength needed to magnetize the core to a flux density \$ B \$. This air gap has a severe disadvantage: within the air gap the relative permeability is reduced to unity and this causes the flux to exit the core and enter the winding, leading to eddy current losses in the winding. The power loss density is concentrated around the air gap, so there is the risk of a hot spot.
Iron powder cores do not need the additional air gap since it is integrated into the material and, in consequence, spread within the complete core volume. This reduces the eddy current losses in the winding and the remaining eddy current losses are distributed throughout the winding length.
Furthermore, energy storage is limited by the saturation flux density. In ferrite this saturation flux density is about 400 mT and decreases with temperature. In iron powder cores saturation flux densities of more than 1 T can be utilized, depending on the material.
As you mentioned Micrometals core: Micrometals, Inc. offers an Inductor Design Software that can be used to design basic inductors including power loss calculations.
If you know what flux density the material saturates at and you know what the BH curve for the mateial is you can calculate H: -
H = \$ \dfrac{ampere \times turns}{effective\space length\space of\space core}\$
The effective length of the core should be quoted in the product spec but for a toroid you can calculate it easily - take the mean radius (R) to the mid-point of the core and use \$2\pi R\$ as that length.
